We undertook a re-analysis of the Canadian data from the thirteen-country INTERPHONE case-control study (2001-2004), which evaluated the association between mobile phone use and risk of brain, acoustic neuroma, and parotid gland tumors. The main publication of the multinational INTERPHONE study concluded that “biases and errors prevent a causal interpretation”. We applied a probabilistic multiple-bias model to address possible biases simultaneously, using validation data from billing records and non-participant questionnaires as information on recall error and selective participation. Our modelling sought to adjust for these sources of uncertainty and to facilitate interpretation. For glioma, the odds ratio comparing highest quartile of use (over 558 lifetime hours) to non-regular users was 2.0 (95% confidence interval: 1.2, 3.4). The odds ratio was 2.2 (95% confidence interval: 1.3, 4.1) when adjusted for selection and recall biases. There was little evidence of an increase in the risk of meningioma, acoustic neuroma, or parotid gland tumors in relation to mobile phone use. Adjustments for selection and recall biases did not materially affect interpretation in our Canadian results.

It is noteworthy that statistically significant increased risk was found already at 558+ hours of cumulative use corresponding to 9 min per day during 10 years. This amount is much lower than now used for wireless phones. Total Interphone showed for cumulative call time, 1640 hours or more, odds ratio 1.40 (95% confidence interval 1.03–1.89) for glioma. This corresponds to less than half an hour per day (27 min) during 10 years.

The Interphone study on use of mobile phones and brain tumour risk included 13 countries during the study period 2000 – 2004. The major results were published after a delay of 6 years in 2010. In the last decile of cumulative exposure > 1,640 h a statistically significant increased risk for glioma was found, OR = 1.40, 95 % CI =1.03-1.89. In the other categories of cumulative use a decreased risk was found. Bias and confounding were discussed as potential reasons for that. Analysing only subjects with regular use of a mobile phone yielded OR = 1.82, 95 % CI = 1.15-2.89 in the group with highest cumulative use.

There was an age difference between cases and controls in the Interphone study and furthermore cases and the matched controls were interviewed at different time periods, controls usually later than cases. This is problematic for mobile phone use with rapid penetration of the use in the population. In a recently published alternative analysis, cases and controls nearest in age and time for interview were included. The association between mobile phone use and glioma was strengthened thereby. Thus, among regular users in the 10th decile (> 1,640 h) cumulative use gave OR = 2.82, 95 % CI = 1.09-7.32. The authors concluded that there was ‘stronger positive association among long-term users and those in the highest categories of cumulative call time and number of calls.’.

Since the IARC evaluation in 2011 on exposure to radiofrequency radiation form mobile phones, and other devices that emit such radiation, and brain tumour risk additional research has strengthened the association. It is by now time to re-evaluate the scientific evidence on the cancer risk from radiofrequency radiation.

In Table 2 five categories for the distance were used with > 115.01 mm as the reference category (α = 1.0). An association with distance from preferred side of mobile phone use to center of tumour was found; the closer the distance the higher the risk. The highest risk was found in the group with the closest distance (0-55 mm) yielding α = 2.37, 95 % Confidence Interval (CI) = 1.56-4.56.

The same association was seen if distance was based on point with highest Specific Absorption Rate (SAR) instead of preferred ear and if using a model assuming that the preferred side of phone use was not exclusively used (“mixing proportion”). The latter model generated higher risk estimates than the other two but with wider confidence intervals.

In Table 3 tumour size, duration of phone use, cumulative phone use, cumulative number of calls were analyzed. Although not statistically significant, higher risks with decreasing distance were found in the upper levels of these dichotomized covariates.

The authors concluded that ‘Taken together, our results suggest that ever using a mobile phone regularly is associated with glioma localization in the sense that more gliomas occurred closer to the ear on the side of the head where the mobile phone was reported to have been used the most. However, this trend was not related to amount of mobile phone use, making it less likely that the association observed is caused by a relationship between mobile phone use and cancer risk.’

The first part although correct is misleading. The correct statement would be that the risk was highest for glioma closer to the ear as would be expected based on the exposure to RF radiation. The last sentence should have indicated that although not statistically significant, the risk was highest in the group with longest duration of phone use, highest cumulative phone use and number of calls. This is a pattern one would expect if there is an association between mobile phone use and glioma.

A similar tendency to not correctly downplaying the association is found in the abstract: ‘The association was independent of the cumulative call time and cumulative number of calls.’ Since many persons read only the abstract, as also presented in PubMed, correct presentation of the results including αs and 95 % CIs would have been more relevant.

The correct interpretation of this study is simply that it confirms an increased risk for glioma associated with mobile phone use.

Footnote: The α values represent the change in risk of observing a tumor within the given interval in comparison with the baseline intensity.